The present invention relates to a color separation optical system and an image display optical system which are used for an image projection apparatus such as a liquid crystal projector and which separate light from a light source into a plurality of light components for colors to direct the light components to light modulation elements such as liquid crystal panels.
To improve the contrast characteristics of images projected by an image projection apparatus, it is necessary to reduce a range of incident angles of a luminous flux entering an optical element such as a polarization beam splitter sensitive to incident angle characteristics in a color separation optical system or a color separation/combination optical system.
Japanese Patent Laid-Open No. H05(1993)-303085 has disclosed an optical system in which light from a light source is divided into a plurality of luminous fluxes by a lens array to form secondary images of the light source, and the plurality of luminous fluxes are caused to overlap on a liquid crystal panel to illuminate it. The optical system is provided with an aperture for limiting the luminous fluxes near the secondary images of the light source to achieve a reduction of a range of incident angles on an optical element sensitive to incident angle characteristics.
Although the optical system disclosed in Japanese Patent Laid-Open No. H05(1993)-303085 can improve the contrast of images, the limitation of the luminous fluxes near the secondary images of the light source significantly decreases the amount of light which illuminates the liquid crystal panel. In other words, the resulting projected image is dark.
In addition, the optical system limits the luminous fluxes at a position closer to the light source than a color separation optical system, so that it cannot limit the luminous fluxes in association with wavelengths and hence is not effective in improving black color and black unevenness in a black display state.